1. Field of the Invention
The present invention relates to a plasma display device and a drive method for use in a plasma display device, and more particularly to a plasma display device that can be advantageously used for improving the level of display luminance in a plasma display panel driven by a so-called subfield method and a drive method adapted for such plasma display device. In the subfield method, one field (period) of the display screen is divided into a plurality of subfields weighted based on the gray scale level.
2. Description of the Related Art
Plasma display devices having a plasma display panel (referred to hereinbelow as “PDP”) as the main component possess a large number of merits such as a small thickness, comparative easiness of manufacturing a large-screen display, a wide view field angle, and a high response rate. For this reason, the plasma display devices have been widely used in recent years for wall-mounted TV sets and public display devices.
Based on the operation system, such plasma display devices can be classified into several categories. The most popular PDP uses an Address Display-period separate (ADS) drive system such that the scan period, in which the display data are written into cells, and the sustain period, in which the discharge is actually carried out and the display is conducted, are completely separated. With such an Address Display-period separation system, all the display data have been written within the scan period, and then the image display (screen display) is conducted by applying the sustain pulses to all the cells at the same time in the sustain period. Therefore, the internal circuitry can be rather simplified and a drive margin can be ensured because the write discharge for writing the display data into cells and the sustain discharge for causing the display do not exist together in the panel. Because of those advantages, the Address Display-period separate drive system is used in plasma display devices that are presently commercialized.
In plasma display devices of this type, for example, as shown in FIG. 14 of the accompanying drawings, there are provided a surface discharge electrode group and n data electrodes 4 (Dj, j=1, 2, . . . , n). The data electrodes 4 extends perpendicularly to the surface discharge electrode group. The surface discharge electrode group includes m scan electrodes 2 (Scani, i=1, 2, . . . , m) and sustain electrodes 3 (Susi, i=1, 2, . . . , m) disposed parallel to each other in the row direction H of the screen on the inner surface of a front substrate (not shown in the figure) in a display panel 1. The n data electrodes 4 are disposed on the inner surface of a rear substrate (not shown in the figure) along the column direction V. One unit cell 5 (also referred to hereinbelow simply as “cell”) is formed in each intersection region of the surface discharge electrode group and data electrodes 4, and a cell group is disposed in the form of a matrix extending in the row direction H and column direction V. In the case of a monochromic display, one cell constitutes one pixel, whereas in the case of a color display, three cells (light-emitting cells of red color R, green color G, and blue color B) constitute one pixel.
FIG. 15 of the accompanying drawings is a cross sectional view of the unit cell 5, taken along the XV-XV line in FIG. 14.
In the unit cell 5, a front substrate 11 and a rear substrate 12 are disposed opposite each other via the prescribed gap. The front substrate 11 is a glass substrate or the like. A scan electrode 2 and a sustain electrode 3 are disposed via a discharge gap 13 on the front substrate 11. A transparent dielectric layer 14 is formed on the scan and sustain electrodes 2 and 3. A protective layer 15 is formed on the transparent dielectric layer 14. The protective layer 15 is composed of MgO or the like, and protects the transparent dielectric layer 14 from discharge. The rear substrate 12 is a glass substrate or the like, and data electrodes 4 are provided on the rear substrate 12 so as to be perpendicular to the scan electrodes 2 and sustain electrodes 3. A white dielectric layer 16 is provided on the data electrodes 4, and a phosphor layer 17 is provided on the white dielectric layer 16. Grid-like barrier ribs 18 are formed, so as to surround each cell, between the front substrate 11 and rear substrate 12. The barrier ribs 18 serve to ensure the discharge space 19 and separate the pixels. A mixed gas of He, Ne, Xe, and the like is enclosed as discharge gas inside the discharge space 19.
FIG. 16 of the accompanying drawings illustrates the principle of the gray scale display method with the Address Display-period separate drive method used in the PDP shown in FIG. 14. Time is plotted against the abscissa and the number of scan electrodes in the PDP is plotted against the ordinate.
In this PDP, as shown in FIG. 16, one field TF is divided into six subfields 1SF, 2SF, . . . , 6SF. Each subfield has its own weighting, depending upon a gray scale level. Each subfield is divided into an initialization period (also called “preliminary discharge period”) T1, a scan period T2, and a sustain period T3. The inclined line in each scan period T2 represents the timing of scan pulses applied in linear succession to the scan electrodes 2. If the scan pulses and data pulses that are applied to the data electrodes 4 are applied at the same time, a write discharge is generated. The sustain period T3 is the period in which the unit cell 5 emits a display light.
In the sustain period T3, sustain pulses are alternately applied to the scan electrodes 2 and sustain electrodes 3, and the cells where the discharge is generated in the scan period T2 emit light with an intensity corresponding to the length of the discharge sustain period T3 (thus, to the number of sustain pulses). In FIG. 16, the lengths of sustain periods T3 of the subfields 1SF, 2SF, . . . 6SF are set to ratios of 1:2:4:8:16:32, and therefore a screen with 64 levels (0-63) of gray scale can be displayed by combining the emission triggered within these sustain periods T3. For example, when a screen with the 29th gray scale level is displayed, the control within the interval of one field TF is so conducted that the subfield 1SF (gray scale level 1), subfield 3SF (gray scale level 4), subfield 4SF (gray scale level 8), and subfield 5SF (gray scale level 16) emit light.
FIG. 17 of the accompanying drawings illustrates the main portion of a drive waveform used in the conventional Address Display-period separate drive system, and FIG. 18(1) to FIG. 18(7) illustrate schematically the arrangement of wall voltage on each electrode in the unit cells 5.
The drive method with the Address Display-period separate drive system will be described below with reference to those drawings.
As shown in FIG. 17, a voltage shown on the waveform Sus is applied to the sustain electrode 3 and a voltage shown by a waveform Scan1 and a voltage shown by a waveform Scan2 are applied to the scan electrode 2. In FIG. 17, the drive waveforms applied to the scan electrodes 2 for two display lines are shown. For the third and subsequent display lines, similar drive waveforms are created by successively shifting the scan pulses a in FIG. 17. A voltage shown by a waveform Data is applied to the data electrode 4. FIG. 18(1) to FIG. 18(7) schematically show the size of the wall voltage on each electrode. A white rectangle located below each electrode indicates a negative wall voltage and a gray rectangle located above the electrode indicates a positive wall voltage. The height of each rectangle indicates the value of the wall voltage. The wall voltage is a voltage generated in a dielectric layer by a wall charge formed on the surface of the dielectric layer located on the electrode by the discharge.
Prior to the initialization period T1 shown in FIG. 17, a sustain period of the previous (preceding) subfield is present and the formation amount of the wall charge, which is a charge accumulated by the discharge on the dielectric layers (transparent dielectric layer 14, white dielectric layer 16) located on each electrode in a unit cell 5, differs, depending on whether or not the sustain discharge has been conducted in the sustain period of that previous subfield. As shown in FIG. 18(1), if the write operation is conducted in a state in which the sustain discharge is still conducted in the sustain period of the previous subfield, the write discharge is sometimes difficult to conduct or it is conducted erroneously under the effect of the above-mentioned different amounts of wall charge formed. For this reason, as shown in FIG. 17, in the initialization period T1, a sustain erase waveform b is applied to the scan electrode 2 and the wall charge generated within the sustain period of the previous subfield is initialized (reset).
In this case, only when a sustain discharge is generated in the sustain period of the previous subfield, a weak discharge is generated between the scan electrode 2 and sustain electrode 3, as shown in FIG. 18(2). Because the weak discharge is continuously generated by the application of a ramp waveform with gradually changing voltage like the sustain erase waveform b in FIG. 17, changes in the wall charge on the electrodes caused by the discharge are small. The weak discharge differs from the discharge at which a rectangular waveform is applied, a strong discharge is at once generated, and the polarity of the wall charge on the electrode is at once inverted. As a result, at the end of the sustain period of the previous subfield, the wall voltage arrangement shown in FIG. 18(3) is assumed, changing from the wall voltage arrangement shown in FIG. 18(2).
In the initialization period T1, a priming effect is produced so that a discharge can easily take place when data are written in a linear succession based on the display data in the scan period T2 following the initialization period T1. In the initialization period T1, also, the wall charge state assumes an optimum state for the write discharge. In this case, the priming waveform c and priming erase waveform d are applied to the scan electrode 2. Because of this priming waveform c, a weak discharge is generated, regardless of the generation of the sustain discharge in the previous subfield, and a state is assumed in which the write discharge is easily generated by the appearance of priming particles in the discharge space 19. Further, because of this priming waveform a, the potential of the scan electrode 2 gradually increases in the positive polarity direction with respect to the potential of the data electrode 4, a negative wall charge increases on the scan electrode 2, a positive wall charge increases on the data electrodes 4, and a wall charge arrangement shown in FIG. 18(4) is assumed. At this time, a state in which a write discharge is easily generated is assumed due to the appearance of priming particles and increase in the wall charge. When a no lit condition is continued for a long time in a certain cell, the number of priming particles decreases and the wall charge decreases. Because of the priming waveform a, however, the number of priming particles and wall charge are compensated (increased) with respect to this state.
The wall charge arrangement shown in FIG. 18(4) is adjusted by the priming erase waveform d, so that the correct drive is possible, and becomes the wall charge arrangement shown in FIG. 18(5). Because of the priming erase waveform d, weak discharges are generated between the scan electrode 2 and sustain electrode 3 and between the scan electrode 2 and data electrode 4. Further, because of the priming erase waveform d, the potential of the data electrode 4 is fixed to a ground potential (GND) and the finally attained value of the potential of the scan electrode 2 becomes almost equal to the potential of the scan pulse a. In the final state of the weak discharge, the wall charge is changed by the discharges so that the two electrodes are at potentials which are almost discharge-triggering values but not the discharge-triggering values (i.e., it's close but the discharge is not generated). Therefore, under the effect of the priming erase waveform d, the quantity of wall charge between the scan electrode 2 and data electrode 4 assumes a value at which no discharge is generated unless a data pulse e is applied when the scan pulse a is applied.
As for the state of the wall charge, if even a small positive pulse is applied to the data electrode 4, the discharge is generated, and the write discharge can be generated by even a data pulse e having a low voltage. However, a certain time actually elapses before a discharge is generated after the voltage is applied. Therefore, in order to generate a discharge within a short pulse such as a scan pulse a, the data pulse e is set to a voltage at a level at which this discharge is generated. Thus, in the initialization period T1, an optimum state is set inside the unit cell 5 with respect to the initialization of the wall charge and write discharge.
In the scan period T2, the state of the wall charge is changed and video information is written into the unit cell 5 by the generation or absence of the write discharge for each scan electrode 2 successively in response to the video signals.
Thus, in the scan period T2, the scan pulses a are successively applied to Scan1, Scan2, . . . , Scanm of the scan electrodes 2. The data pulse e is applied according to the display pattern to D1, D2, . . . , Dn of the data electrodes 4 in response to the scan pulses a. The inclined line of the data pulse e in FIG. 17 indicates whether the data pulse e is applied or not applied by the video signal.
The write discharge is conducted as follows. When the data pulse e is applied, the difference in potential between the scan electrode 2 and data electrode 4 is Vd. At this time, in the initialization period T1, as described hereinabove, a negative wall charge and a positive wall charge are formed on the scan electrode 2 and data electrode 4, respectively, and in the discharge space between the scan electrode 2 and data electrode 4, a wall voltage, which is the voltage applied to the dielectric layer due to those wall charges, is superimposed on the potential difference between the electrodes. As a result, a high voltage is applied. Thus, a write discharge is generated between the scan electrode 2 and data electrode 4. At this time, because of a large difference in potential between the scan electrode 2 and sustain electrode 3, if a write discharge is generated between the scan electrode 2 and data electrode 4, a surface discharge is induced between the scan electrode 2 and sustain electrode 3, as shown in FIG. 18(6), and a positive wall charge and a negative wall charge are accumulated on the scan electrode 2 and sustain electrode 3, respectively, as shown in FIG. 18(7). On the other hand, in the pixels to which the data pulse e is not applied, the difference in potential applied to the discharge space between the scan electrode 2 and data electrode 4 does not exceed the discharge start voltage, so that no discharge is generated and the state of the wall charge does not change. Thus wall charge states of two type occur depending on the presence or absence of the data pulse e.
After the scan pulse a has been applied to all the scan electrodes 2, a transition is made to the sustain period T3. In the sustain period T3, the sustain pulse f is alternately applied to all the scan electrodes 2 and all the sustain electrodes 3. The voltage value Vs of the sustain pulse f is so adjusted that the wall voltage in the vicinity of the discharge gap 13 between the scan electrode 2 and sustain electrode 3 is almost equal in the pixels where the write discharge is not generated, and only the Vs, which is the difference in potential between the two electrodes, is applied to the discharge space between the scan electrode 2 and sustain electrode 3. Thus, a surface discharge is not started between the two electrodes. On the other hand, in the pixels where the write discharge is generated, a positive wall charge is present on the scan electrode 2 and a negative wall charge is present on the sustain electrode 3. Therefore, those positive and negative wall charges are superimposed on the initial positive sustain pulse (first sustain pulse) applied to the scan electrode 2, and the voltage equal to or higher than the discharge start voltage is applied to the discharge space. Thus, the sustain discharge is generated. Because of this discharge, a negative wall charge is accumulated on the scan electrode 2 and a positive wall charge is accumulated on the sustain electrode 3. The next sustain pulse (second sustain pulse) is applied to the sustain electrode 3 and the above-described superposition of the wall charges occurs. Thus, the sustain discharge is here also generated and a wall charge of the polarity opposite to that of the first sustain pulse is accumulated on the scan electrode 2 and sustain electrode 3.
Discharges are thereafter continuously generated based on the same principle. In other words, the difference in potential caused by the wall charge induced by the sustain discharge of the x-th cycle is superimposed on the sustain pulse of the (x+1)-th cycle and the sustain discharge is maintained. The luminance of light emission is determined by the number of continuous cycles of the sustain discharge.
The following problems are associated with the Address Display-period separation system.
In the Address Display-period separation system, the light emission discharge for display is conducted only in the sustain period T3, but one field for one screen display is generally fixed to 16.6 msec ( 1/60 sec). Therefore, when the number of scan lines is high, for example, as in high-resolution displays, the scan period T2 is large and the sustain period T3 shortens correspondingly. If the sustain period T3 becomes shorter, the number of light emission discharges is decreased and the display luminance is reduced.
An Address-While-Display (AWD) drive system is a drive system designed to resolve the above-described problems.
The Address-While-Display drive system uses a PDP of the same structure as that of the Address Display-period separate drive system illustrated by FIGS. 14 and 15, but the scan pulses are applied at the same timing as the sustain pulses. As shown in FIG. 19, one field TF is divided, for example, into six subfields 1SF, 2SF, . . . , 6SF, and one subfield include three pulses: initialization pulse, scan pulse, and sustain pulse. These pulses are applied with a successive shift of the subfields for each scan electrode.
FIG. 20 of the accompanying drawings illustrates the main portion of the drive waveform used in the Address-While-Display drive system.
As shown in FIG. 20, the voltage shown in a waveform Sus is applied to the sustain electrodes 3, and the voltage shown in a waveform Scan1 and the voltage shown in a waveform Scan2 are applied to the scan electrodes 2. FIG. 20 shows the scan electrodes 2 for two display lines only. Similar drive waveforms are applied to the third and subsequent display lines, with a successive shift of scan pulses a. A voltage shown on the waveform Data is applied to the data electrode 4.
FIG. 21(1) to FIG. 21(6) of the accompanying drawings are a series of schematic drawings illustrating the size of the wall voltage on each electrode in the Address-While-Display drive system.
The drive method with the Address-While-Display drive system will be described below with reference to FIG. 21(1) to FIG. 21(6) as well as FIG. 20.
FIG. 21(1) to FIG. 21(6) show the wall voltage in a cell at the six different timing when the Scan1 waveform shown in FIG. 20 is applied to the cell at the timing (1) to (6) in FIG. 20.
As shown in FIG. 20, a pulse of a negative polarity immediately preceding the initialization pulse g is the very last sustain pulse f of the previous subfield, and the very last sustain pulse f is applied at the timing (1). When a sustain discharge is generated in the previous subfield, a sustain discharge is also generated between the scan electrode 2 and sustain electrode 3 at the timing (1) and the wall voltage arrangement changes from the state shown in FIG. 21(1) to that shown in FIG. 21(2).
Then, the initialization pulse g is applied. The state of the wall charge in the unit cell 5 before the initialization pulse g differs depending on whether or not a sustain discharge is generated in the previous subfield. Thus, if the write operation is conducted in a state in which a sustain discharge is generated in the previous subfield, then the write discharge is sometimes difficult to conduct or the writing is conducted erroneously under the effect of this different wall charge. The role of the initialization pulse g is to initialize a state of the wall charge on the dielectric layer in the unit cell 5 that differs depending on the presence or absence of the sustain discharge in the previous subfield. At the timing (2), a sustain pulse f is applied to the sustain electrode 3 at the same time as the initialization pulse g is applied to the scan electrode 2. As a result, a voltage larger than the voltage created upon application of the preceding sustain pulse f is applied between the scan electrode 2 and sustain electrode 3, and a surface discharge is generated between the two electrodes. Then, as shown in FIG. 21(3), wall voltages larger than those during the usual sustain discharge are formed on both the scan electrode 2 and sustain electrode 3.
In the case where only the usual sustain pulse f is then applied, the discharge is not generated during a rise at the pulse end. However, a large wall voltage is formed due to the application of the initialization pulse g. Thus, when both the scan electrode 2 and sustain electrode 3 assume a ground (GND) potential at the end point of the sustain pulse f and initialization pulse g, a voltage equal to or higher than the discharge start voltage is applied by the wall voltage to the discharge space 19 and the surface discharge is generated again. At this time, all the electrodes, including the data electrode 4, are at the GND potential. Therefore, after the discharge end, as shown in FIG. 21(4), the wall voltage is almost absent. In this state, the initiation ends.
Then, a scan pulse a is applied to the scan electrode 2 and writing is conducted. In this writing, the state of wall charges is changed in response to the video signal depending on the presence or absence of the write discharge generation and the video information is written into the unit cell 5 successively for each scan electrode 2. In this case, at the timing (4) shown in FIG. 20, the data pulse e is applied according to the video signal to the data electrode 4 synchronously with the scan pulse a. The inclined line in the data pulse e indicates whether or not the data pulse e is applied, based on the video signals. If the data pulse e is applied, a high voltage exceeding the discharge start voltage is applied between the scan electrode 2 and data electrode 4 and, as shown in FIG. 21(4), an oppositely directed discharge is generated between the two electrodes. At this time, a large difference in potential is also present between the scan electrode 2 and sustain electrode 3, so that if a write discharge is generated between the scan electrode 2 and data electrode 4, a surface discharge is induced between the scan electrode 2 and sustain electrode 3 and, as shown in FIG. 21(5), a positive wall charge is accumulated on the scan electrode 2 and a negative wall charge is accumulated on the sustain electrode 3.
On the other hand, in the cell to which the data pulse e is not applied, the difference in potential that is applied to the discharge space between the scan electrode 2 and data electrode 4 does not exceed the discharge start voltage. Therefore, no discharge is generated and the state of wall charge does not change. Thus, the states of wall charges of two types can be produced depending on whether the data pulse e is present or absent. At this time, the scan pulse a is applied at the same timing as the sustain pulse f is applied to the other scan electrode. For example, at the timing (6) shown in FIG. 20, a sustain pulse f shown on the waveform Scan1 is applied and a scan pulse a shown on the waveform Scan2 is applied. Writing has to be conducted for each scan electrode. Thus, even if the scan pulse a and sustain pulse f are applied at the same timing, the write discharge has to be generated only with the scan electrode to which the scan pulse a is applied. For this reason, the voltage Vw of the scan pulse a is set to a value with a negative polarity greater than that of the sustain voltage Vs. Due to the increase in the voltage, write discharge is generated only at the scan electrode to which the scan pulse a is applied. However, in the case where the data pulse e is not applied, the generation of discharge has to be prevented. Therefore, the voltage Vw of the scan pulse a cannot be set to a value over the discharge start voltage between the scan electrode 2 and sustain electrode 3.
The pulse width of the scan pulse a is wider than the sustain pulse f and ends at the timing (5) the next sustain pulse f is applied to the sustain electrode 3. At the timing (5), if the scan pulse a rises, the data pulse e also ends at the same time, and a write discharge is generated, then a discharge in the opposite direction is generated between the scan electrode 2 and data electrode 4 by the wall voltage formed upon this write discharge. Separately therefrom, because the sustain pulse f is applied to the sustain electrode 3, a discharge is also generated between the scan electrode 2 and sustain electrode 3. As a result, the wall voltage arrangement changes from the state shown in FIG. 21(5) to that shown in FIG. 21(6). Then, the surface discharge is generated each time the sustain pulse f is applied, and the wall voltage arrangement states shown in FIG. 21(5) and FIG. 21(6) are alternately repeated.
On the other hand, when the data pulse e is not applied and the write discharge is not generated, the wall voltage remains in the state shown in FIG. 21(4), and no discharge is thereafter generated even if the sustain pulse f is applied. As described hereinabove, the states with and without the generation of the sustain discharge can be switched by applying or not applying the data pulse e. In such an Address-While-Display drive system, the scan pulse a can be superimposed in time on the sustain pulse f. Therefore, the interval in which the scan pulse a is applied to the other scan electrode can be allocated to the sustain discharge generation interval. As a consequence, all the pulses other than the initialization pulse g and scan pulse a of the scan electrode can be allocated to the application interval of the sustain pulse f. Furthermore, a major portion of one field can be allocated to the sustain period. Therefore, the display luminance level is increased by increasing the number of sustain pulses.
FIG. 22 illustrates the main portion of the drive waveform used in another Address-While-Display drive system.
In the drive method with this Address-While-Display drive system, as shown in FIG. 22, the sustain pulse f assumes a positive polarity. Furthermore, the initialization pulses h, j are successively applied to the scan electrode 2. The initialization pulse h is larger than the voltage Vs of the sustain pulse. When a scan pulse a is applied, other scan electrodes may be at a GND potential, and therefore a potential has to be decreased below the GND potential in order to generate the write discharge only with the scan electrode to which the scan pulse a is applied. However, similar to the case of the drive waveform shown in FIG. 20, the surface discharge must not be generated between the scan electrode 2 and sustain electrode 3 merely by introducing the scan pulse a. Therefore, the sum of the voltage Vs of the sustain pulse f and the voltage Vw of the scan pulse a cannot be set so as to exceed the discharge start voltage. The states of the wall voltage at timings (1) to (6) in FIG. 22 are shown in FIGS. 23(1) to 23(6), respectively.
In addition to the above-described drive systems, there is a scan-sustain mix drive system. One example of the scan-sustain mix drive systems is a drive method for a gas discharge panel disclosed in Japanese Patent Kokai (Laid-open Application No. 2000-122603 (Abstract and FIG. 4). With the drive method described in Japanese Patent Kokai No. 2000-122603, a scan pulse is applied between a certain sustain pulse and another sustain pulse, so as to avoid overlapping in time. In this case, because the scan pulse and sustain pulse are not applied at the same timing, the write discharge is generated only at the scan electrode to which a scan pulse is applied.
In the display device described in Japanese Patent Application Kokai No. 2000-112430 (Abstract and FIG. 3), a drive method is employed that is similar to that described in Japanese Patent Kokai No. 2000-122603.
The following problems are associated with the above-described conventional plasma display devices.
With the Address-While-Display drive system, the major portion of the one field interval is allocated to the sustain discharge and a high display luminance is obtained. However, because the scan pulse a is applied at the timing the sustain pulse f is applied to the other scan electrode, a voltage larger than the sustain pulse f has to be applied so that the write discharge is generated only at the scan electrode to which the scan pulse a has been applied. In other words, a voltage Vw of the scan pulse has to be set in addition to the voltage Vs of the sustain pulse f. Therefore, it is necessary to set more voltages than in the case of Address Display-period separate drive system, the scale of the power source circuit is increased, and the scale of the scan electrode drive circuit (not shown in the figure) is also increased. Furthermore, as shown in FIG. 20, the voltage Vw of the scan pulse is a negative voltage greater than the voltage Vs of the sustain pulse and has to be set to a voltage at which no discharge is generated when the data pulse e is not applied. Also, the voltage Vs of the sustain pulse has to be a relatively large value so that the sustain discharge continues each time the potential is inverted. Thus, the range of the voltage Vw of the scan pulse is significantly narrowed and the drive margin cannot be widened.
In the case shown in FIG. 22, too, the level of the scan pulse a is such that the potential difference (Vw) from the GND level is less than the scan pulse voltage Vw shown in FIG. 20, but the initialization pulse h becomes a positive voltage larger than the voltage Vs of the sustain pulse. Similar to the scan pulse a, the initialization pulse h is also supplied in a linear succession to each scan electrode, so that the output from the scan electrode drive circuit is necessary, and the scan electrode drive circuit has to withstand the voltage of the initialization pulse h. In either of the cases illustrated by FIG. 20 and FIG. 22, both application of the data pulse e and application of the scan pulse a should be required to generate the discharge; it is necessary to prevent the surface discharge from generating between the scan electrode 2 and sustain electrode 3 when the scan pulse a is only applied. For this purpose, it is necessary to prevent the difference in potential between the scan electrode 2 and sustain electrode 3 from exceeding the discharge start voltage of the surface when scan pulses a are applied.
On the other hand, in order to conduct writing with scan electrodes to which scan pulses a are applied, the potential of the scan pulse a has to be lower than the potential of other scan electrodes. As a result, it is necessary to apply a voltage equal to or higher than the voltage of the sustain pulse between the scan electrode 2 and sustain electrode 3. The voltage of the sustain pulse has to be sufficiently high so as to maintain the sustain pulse. Thus, voltage setting of the scan pulse a can be conducted only within a certain limited range, which results in a narrowed drive margin.
With the scan-sustain mix drive system described in Japanese Patent Kokai Nos. 2000-122603 and 2000-112430, the sustain pulse and scan pulse overlap in time. Therefore, the number of sustain pulses in one field is equal to that of the Address Display-period separate drive system and the luminance level is difficult to increase, as in the Address-While-Display drive system.